1. Field of the Invention
The present invention is directed to methods for reducing the shrinkage of wool during a wetting and/or laundering stage. More particularly, the present invention provides for a method of reducing the shrinkage of wool during wet processing by contacting the wool substrate with an oxidoreductase enzyme.
2. State of the Art
The conversion of raw wool into a textile fabric or garment involves a long series of separate processes. Generally, there are two main processing systems, worsted and woolen, and another process termed short-staple or semi-worsted which is used generally in carpet production. Many wool treatment processes involve, in the following order, scouring, carding, spinning, weaving, piece dyeing and finishing (see FIG. 1). During these steps, uncontrolled shrinkage can be a problem.
Wool, in a wet state, which is submitted to any form of mechanical action including compression and relaxation undergoes a process known as felting. The phenomenon consists of individual fibers packing themselves closer and closer together, until what was originally a comparatively soft structure becomes a hard mass of interlocking fibers. This increase in density is naturally accompanied by a decrease in area or volume, commonly described as shrinkage. Felting provides both desirable and undesirable properties to wool; valuable in contexts where it is desirable to close up the texture and increase the bulkiness of the cloth (i.e., hats and jackets), but objectionable in garments which are washed frequently and for which shrinkage would make the article less desirable or unusable. Felting is generally believed to result from a directional friction effect which is connected with the structure of epithelial scales incorporated into the wool fiber itself (see e.g., E. R. Trotman, "Dyeing and Chemical Technology of Textile Fibers", 6th Ed., pp. 218 et seq., (Wiley-Interscience Publications, New York, 1984)).
In the textile industry, various treatments have been developed to reduce shrinkage. These treatments were classified in four categories by Trotman, supra, comprising: (1) modifying the scale structure of the wool fiber in such a way so as to reduce or eliminate the directional friction effect; (2) introducing intermolecular cross-links, thereby decreasing elasticity; (3) covering the fibers with a film which masks the surface, thereby removing the cause of the directional friction effect; and (4) "spot-welding" with a polymer which cements the yarn or fibers at the points of intersection, giving a rigid scaffold which imposes a severe limitation on the possibility of dimensional change. With respect to the first category, modifying the scale structure of the wool fiber, the oldest method involves applying chlorine based compounds, such as gaseous chorine, sodium hypochlorite or dichloroisocyanuric acid, to the wool surface. While it was originally believed that the success of this process was due to the breaking of disulphide bonds within the wool structure, Trotman states that this was an oversimplification of the true situation. Other fiber modification processes for wool treatment include the use of potassium permanganate in conjunction with hypochlorite at pH 11 (GB Patent No. 569,730); treating with sodium sulphate at a pH of less than 2 (known as the International Wool Secretariat process); and treating with permonosulphuric acid (generally at a pH of less than 2). Efforts to reduce shrinkage by the application of a polymer have included using hexamethylenediamine in a first stage and sebacoyl chloride in a second stage, known as the "graft polymerization method".
While these processes have been commercially accepted, there have been numerous problems with the use of currently used chemicals as wool shrink proofing agents. For example, strong acids, chlorine and chlorine based compounds are known for their difficulty as a waste product and their detrimental effect on the environment. Moreover, the use of chlorine has had the tendency to result in a less desirable wool product in terms of appearance and feel. Also, the chlorine processes have the tendency to increase the substantivity of the wool, making dye absorption rapid and resulting in difficulty in achieving level dye shades.
To overcome these difficulties in the prior art chemical based processes, the industry has looked for alternatives. One such alternative which has developed is the use of proteases to modify the scales of the wool fibers and confer resistance to felting shrinkage (see e.g., PCT Publication No. WO 96/19611; Levene et al., ISDC, vol. 112, pp. 6-10 (January 1996)). However, with some very specific exceptions, when protease is applied under conditions capable of reducing shrinkage within the limits required for machine washability, the process has resulted in significant fiber damage. Levene suggests the use of sodium sulphite at pH 8.5-9.0 prior to the application of the protease with or without an optional preliminary mild oxidation step using peroxymonosulphuric acid, dichloroisocyanuric acid or monoperoxyphthalic acid. However, none of the protease treatments disclosed was found to confer adequate shrink-resistance without causing excessive damage to the fibers. Other processes which have been suggested to reduce felting in wool include plasma treatment (see e.g., Thomas et al., Environmentally Friendly Finishing Processes for Wool by Pretreatment with Electrical Discharges in Gas (Plasma), International Textile Bulletin, vol. 2 (1993); Japanese Patent Application Tokkai Hei 4-327274) and the Delhey process wherein wool is treated with an aqueous solution of hydrogen peroxide in the presence of wolframate, optionally followed by treatment in a solution or dispersion of synthetic polymers.
Peroxidases and oxidases have been suggested for use in the treatment of textiles for bleaching, dye transfer inhibition or to remove excess dye from new textiles (EP Publication No. 0 495 836; PCT Publication Nos. WO 92/18683 and WO 92/18687) and as an additive to detergent for bleaching stains (PCT Publication No. 89/09813).
PCT Publication Nos. WO 96/12845 and 96/12846 disclose processes for providing a bleached look in the colour density of the surface of dyed fabrics, particularly cellulosic fabrics such as denim, comprising using a phenol oxidizing enzyme such as a peroxidase or a laccase and an enhancing agent.
While significant progress has been achieved with the use of chemicals in the wool industry to prevent shrinkage, as described above, the need remains for an environmentally benign, effective and safe method of conferring shrink-resistance to wool.